1. Field of the Invention
The present invention relates to a tape cassette such as an audio tape cassette, a tape cassette halves forming mold for using a nesting pin mounted into a mold half to provide connecting portions of coupled upper and lower halves forming a casing of such a tape cassette, and a method for using the cassette halves prepared with the mold to prepare such a tape cassette.
2. Discussion of Background
An audio tape cassette has been used in such a manner that a magnetic tape wound on hubs is housed in a casing composed of upper and lower halves. The upper and lower halves include base plates 11 and 21 which has vertical surrounding side plates 12 and 22 of substantially equal height, as shown in FIG. 26 (the upper half 10) and FIG. 27 (the lower half 20). The base plates 11 and 21 have central portions formed with tape quantity observing windows 13 and 23 and hub shaft inserting holes 14 and 24, and an open side to receive a head formed with head house portions 15 and 25 which project like platforms. The base plates 11 and 21 have four corners formed connecting portions 16 and 26, by means of which the base plates are coupled together by machine screws. There are provided similar connecting portions 17 and 27 in a central portion behind the head house portions 15 and 25, cassette positioning holes 18 and 28 on both sides of the connecting portions 17 and 27, and capstan inserting holes 19 and 29. On the base plate 21 is provided casing strengthening bosses 30 and 31 at locations near to the head house portion 25 just behind the central connecting portion 27 and far behind the central connecting portion.
In order to clarify the shape and structure of the lower half 20, in particular the shapes and structures of the hub shaft inserting holes 24, the corner connecting portions 26, the central connecting portion 27 and the casing strengthening bosses 30, 31 and the like, there are shown a plan view of the lower half 20 in FIG. 28, and a cross-sectional view taken along a section line 29--29 of FIG. 28 in FIG. 29. As clearly shown in FIGS. 28 and 29, the corner connecting portions 26 and the central connecting portion 27 are similar circular posts with the same diameter and tapped holes. However, the central connecting portion 27 has the opening of the hole formed at a higher level and the hole formed deeper than those of the corner connecting portions 26. The casing strengthening boss 30 at the front side is a long, slender circular post, whereas the casing strengthening boss 31 at the rear side is a thick cylindrical post. The connecting portions 26 on the four corners of the base plate 21 have the same structure.
A corner connecting portion 16 of the upper half 10 which corresponds to a corner connecting portion 26 of the lower half 20 has a structure shown in FIG. 30. The other corner connecting portions 16 and the central connecting portion 17 of the upper half 10 have the same or substantially the same structure as the corner connecting portion 16 shown in FIG. 30. The upper and lower halves 10 and 20 are separately prepared by using different molds which comprise a cavity and a core. The respective halves 10 and 20 are independently molded by means of injecting molding of plastics. In such a molding process, when the corner connecting portions 16 are formed, a mold 40 for molding the upper half 10 has nesting pins 50a and 50b fitted into the cavity 40a and the core 40b to form connecting portions for machine screw connection as shown in FIG. 31. The other connecting portion 17 is also formed by using the same or substantially the same nesting pins 50a and 50b. When the corner connecting portions 26 are formed, a mold 60 for forming the lower half 20 has no nesting pin fitted into the cavity 60a, and have a nesting pin 70a fitted into the core 60b to form the connecting portions for machine screw connection as shown in FIG. 32. The other connecting portion 27 is also formed by using the same or substantially the same nesting pin as the nesting pin 70a.
When the upper and lower halves 10 and 20 have the connecting portions 16, 17, 26 and 27 at five spots, respectively, and the corresponding connecting portions are connected by machine screws, the upper and lower halves 10 and 20 are firmly connected together to provide a casing, and have an advantage in that disassembling is possible when a problem occurs. However, connecting the upper and lower halves 10 and 20 by using of machine screws causes a product to be costly and prevents production rate from increasing. In order to cope with those problems, methods for connecting the upper and lower halves by melt-bonding have been proposed in Japanese Examined Patent Publication No. 16644/1975, Japanese Unexamined Utility Model Publication No. 102085/1982, Japanese Unexamined Utility Model Publication No. 57786/1991, Japanese Unexamined Utility Model Publication No. 36671/1993 and so forth. Such melt-bonding methods are roughly divided into measures to provide pillar-shaped projections at four corners and at the locations of the head house portions of upper and lower halves, which correspond to the conventional connecting portions for machine screw connection, and carry out melt-bonding at those locations, and measures to provide ridges on tipped surfaces of side plates of upper and lower halves and to subject those ridges to melt-bonding.
However, the latter melt-bonding method, i.e. the measure to provide melt-bonding ridges on the tipped surfaces of the side plates creates a problem in that when the upper and lower halves are matched and melt-bonded together, a part of the melted ridges is likely to squeeze out and misalignment of the upper and lower halves can occur. With respect to this point, the former melt-bonding method does not create such a problem, though a new tape cassette casing mold for melt-bonding is required, creating a great problem in the expense of the mold.
Although it is thought out that only the connecting portions at the corners are melt-bonded without melt-bonding the surrounding portions of the halves which are good in appearance, there are problems in that a bonding force is inevitably so poor that the connecting portions are likely to be separated or damaged due to dropping or other shocks, and are less durable, and that the value of a product can lower due to the presence of a gap or shrinkage in appearance.